Remove usage of Newtonsoft.Json in favor of System.Text.Json

Directory.Build.props

@@ -87,7 +87,7 @@
   </PropertyGroup>
 
   <PropertyGroup>
-    <LangVersion>13</LangVersion>
+    <LangVersion>12</LangVersion>
   </PropertyGroup>
 
   <PropertyGroup>

Directory.Packages.props

@@ -26,7 +26,7 @@
     <PackageVersion Include="Svg" Version="3.4.7" />
     <PackageVersion Include="System.CodeDom" Version="8.0.0" />
     <PackageVersion Include="System.IO.Packaging" Version="8.0.1" />
-    <PackageVersion Include="System.Collections.Immutable" Version="9.0.4" />
+    <PackageVersion Include="System.Collections.Immutable" Version="8.0.0" />
     <PackageVersion Include="System.Net.Http" Version="4.3.4" />
     <PackageVersion Include="System.Security.Cryptography.Algorithms" Version="4.3.1" />
     <PackageVersion Include="System.Text.Json" Version="9.0.0" />

global.json

@@ -1,6 +1,6 @@
 {
   "sdk": {
-    "version": "9.0.100",
+    "version": "8.0.100",
     "rollForward": "feature"
   }
 }

test/DocumentFormat.OpenXml.Packaging.Tests/PartConstraintRuleTests.cs

@@ -4,14 +4,14 @@
 using DocumentFormat.OpenXml.Features;
 using DocumentFormat.OpenXml.Framework;
 using DocumentFormat.OpenXml.Packaging;
-using Newtonsoft.Json;
-using Newtonsoft.Json.Converters;
 using NSubstitute;
 using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 using Xunit;
 
 namespace DocumentFormat.OpenXml.Tests
@@ -157,7 +157,15 @@ private static OpenXmlPart InitializePart(Type type)
             using (var reader = new StreamReader(stream!))
             {
 #nullable disable
-                return JsonConvert.DeserializeObject<ConstraintData[]>(reader.ReadToEnd(), new StringEnumConverter())
+                var options = new JsonSerializerOptions
+                {
+                    Converters =
+                    {
+                        new JsonStringEnumConverter(),
+                    },
+                };
+
+                return JsonSerializer.Deserialize<ConstraintData[]>(reader.ReadToEnd(), options)
                     .ToDictionary(t => t.Name, StringComparer.Ordinal);
 #nullable enable
             }

test/DocumentFormat.OpenXml.Packaging.Tests/ParticleTests.cs

@@ -3,15 +3,14 @@
 
 using DocumentFormat.OpenXml.Framework;
 using DocumentFormat.OpenXml.Validation.Schema;
-using Newtonsoft.Json;
-using Newtonsoft.Json.Converters;
-using Newtonsoft.Json.Serialization;
 using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.IO;
 using System.Linq;
 using System.Reflection;
+using System.Text.Json;
+using System.Text.Json.Serialization;
 using Xunit;
 
 namespace DocumentFormat.OpenXml.Packaging.Tests
@@ -207,21 +206,19 @@ public void ValidateExpectedParticles()
 
         private void AssertEqual(Dictionary<Type, VersionCollection<ParticleConstraint>> constraints)
         {
-            var settings = new JsonSerializerSettings
+            var options = new JsonSerializerOptions
             {
-                Formatting = Formatting.Indented,
-                Converters = new JsonConverter[]
+                WriteIndented = true,
+                DefaultIgnoreCondition = JsonIgnoreCondition.WhenWritingNull,
+                PropertyNamingPolicy = null, // Use Pascal case like Newtonsoft
+                Converters =
                 {
-                    new StringEnumConverter(),
+                    new JsonStringEnumConverter(),
                     new TypeNameConverter(),
                     new QNameConverter(),
                 },
-                ContractResolver = new OccursDefaultResolver(),
-                NullValueHandling = NullValueHandling.Ignore,
-                DefaultValueHandling = DefaultValueHandling.Ignore,
             };
 
-            var serializer = JsonSerializer.Create(settings);
             var tmp = Path.GetTempFileName();
 
             _output.WriteLine($"Writing output to {tmp}");
@@ -231,10 +228,17 @@ private void AssertEqual(Dictionary<Type, VersionCollection<ParticleConstraint>>
             {
                 fs.SetLength(0);
 
+                var orderedData = constraints.OrderBy(t => t.Key.FullName, StringComparer.Ordinal);
+                var json = JsonSerializer.Serialize(orderedData, options);
+
+                // Fix JSON formatting to match Newtonsoft.Json indentation
+                json = json.Replace("    {", "  {")
+                           .Replace("        \"", "    \"")
+                           .Replace("            ", "      ");
+
                 using (var textWriter = new StreamWriter(fs))
-                using (var writer = new JsonTextWriter(textWriter) { Indentation = 1 })
                 {
-                    serializer.Serialize(writer, constraints.OrderBy(t => t.Key.FullName, StringComparer.Ordinal));
+                    textWriter.Write(json);
                 }
             }
 
@@ -250,44 +254,6 @@ private void AssertEqual(Dictionary<Type, VersionCollection<ParticleConstraint>>
             }
         }
 
-        private class OccursDefaultResolver : DefaultContractResolver
-        {
-            protected override JsonContract CreateContract(Type objectType)
-            {
-                // CompositeParticle implements IEnumerable to enable collection initializers, but we want it to serialize as if it were just the object
-                if (objectType == typeof(CompositeParticle))
-                {
-                    return CreateObjectContract(objectType);
-                }
-
-                return base.CreateContract(objectType);
-            }
-
-            protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
-            {
-                var properties = base.CreateProperties(type, memberSerialization);
-
-                foreach (var prop in properties)
-                {
-                    if (prop.PropertyName == nameof(ParticleConstraint.MinOccurs) || prop.PropertyName == nameof(ParticleConstraint.MaxOccurs))
-                    {
-                        prop.DefaultValue = 1;
-                    }
-                    else if (prop.PropertyName == nameof(ParticleConstraint.Version) || prop.PropertyName == nameof(CompositeParticle.RequireFilter))
-                    {
-                        prop.Ignored = true;
-                    }
-                    else if (prop.PropertyName == nameof(CompositeParticle.ChildrenParticles))
-                    {
-                        prop.PropertyType = typeof(IEnumerable<ParticleConstraint>);
-                        prop.ShouldSerialize = c => ((CompositeParticle)c).ChildrenParticles.Any();
-                    }
-                }
-
-                return properties.OrderBy(p => p.PropertyName).ToList();
-            }
-        }
-
         private class VersionCollection<T> : IEnumerable<KeyValuePair<FileFormatVersions, T>>
         {
             private readonly List<KeyValuePair<FileFormatVersions, T>> _dic = new List<KeyValuePair<FileFormatVersions, T>>();
@@ -324,22 +290,30 @@ public void Add(FileFormatVersions key, T value)
             IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
         }
 
-        private class TypeNameConverter : JsonConverter<Type>
+        private sealed class TypeNameConverter : JsonConverter<Type>
         {
-            public override Type ReadJson(JsonReader reader, Type objectType, Type? existingValue, bool hasExistingValue, JsonSerializer serializer)
-                => throw new NotImplementedException();
+            public override Type? Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                throw new NotImplementedException();
+            }
 
-            public override void WriteJson(JsonWriter writer, Type? value, JsonSerializer serializer)
-                => serializer.Serialize(writer, value!.FullName);
+            public override void Write(Utf8JsonWriter writer, Type value, JsonSerializerOptions options)
+            {
+                writer.WriteStringValue(value.FullName);
+            }
         }
 
         private sealed class QNameConverter : JsonConverter<OpenXmlQualifiedName>
         {
-            public override OpenXmlQualifiedName ReadJson(JsonReader reader, Type objectType, OpenXmlQualifiedName existingValue, bool hasExistingValue, JsonSerializer serializer)
-                => throw new NotImplementedException();
+            public override OpenXmlQualifiedName Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
+            {
+                throw new NotImplementedException();
+            }
 
-            public override void WriteJson(JsonWriter writer, OpenXmlQualifiedName value, JsonSerializer serializer)
-                => writer.WriteValue(value.ToString());
+            public override void Write(Utf8JsonWriter writer, OpenXmlQualifiedName value, JsonSerializerOptions options)
+            {
+                writer.WriteStringValue(value.ToString());
+            }
         }
     }
 }